1. Field of the Invention
The present invention relates to the field of semiconductor devices and more particularly to a method for forming a reliable, low-defect, thin dielectric layer.
2. Art Background
In the semiconductor industry, dielectric films, such as silicon dioxide films (S.sub.i O.sub.2, also called "oxide" films) are used in a variety of applications. One important use of an oxide layer is as a gate oxide disposed between the gate of an MOS device and a channel region in the device. In recent years, as device dimensions are scaled to provide for high density and high performance devices, it has become increasingly important to provide extremely thin, reliable, low-defect and manufacturable gate oxides. For example, gate oxides as thin as approximately 25 .ANG. are currently under development.
Oxide layers have been treated with nitrogen containing compounds to improve transistor hot electron reliability. In addition to the improved hot electron reliability, these oxides are insensitive to radiation and provide a barrier to various dopants, such as boron, and contaminants. The treatment may include exposing an oxide film to a compound containing chemically active nitrogen, or forming the oxide film in the presence of such compound. The resulting film typically comprises nitrogen incorporated therein, and may be represented by the formula Si.sub.x O.sub.y N.sub.z. It will be appreciated that the chemical structure and composition may vary depending upon the process, and in a given process may vary throughout the film. Regardless of the chemical structure and composition of the film, all such films are referred to as "nitrided oxides" herein. The nitrided oxides have been produced by furnace or rapid thermal processing (RTP) oxidation using nitrous oxide (N.sub.2 O). Alternatively, a dry oxide using furnace or rapid thermal processing may be formed followed by nitridation using N.sub.2 O, or ammonia (NH.sub.3), or a combination of both in a furnace or RTP system. If desired, the nitrided oxide may then be reoxidized using dry O.sub.2 or N.sub.2 O in a furnace or RPT system. However, these methods have proved to be not manufacturable because of high defect density of the nitrided oxide and/or poor thickness uniformity and control. In addition to the manufacturability problems, the nitridation process is also known to lead to the formation of a large number of electron traps, interface states, high fixed positive charge density, and a susceptibility to stress induced interface state formation, all of which have a deleterious effect on device performance.
What is needed is a manufacturable method of forming a nitrided oxide. The nitrided oxide should have low-defect density, and good thickness uniformity and control. Furthermore, the process should be capable of producing a very thin oxide. Moreover, it is desirable that the oxide may be useful as, for example, a gate oxide, a spacer oxide, a composite oxide or a portion of a trench oxide.